Limitations of the transpulmonary indicator dilution method for assessment of preload changes in critically ill patients with reduced left ventricular function

Abstract

Objective: We examined whether intrathoracic blood volume (ITBV) and total end-diastolic volume (TEDV), determined by the transpulmonary indicator dilution technique, adequately reflect preload changes during fluid administration in patients with reduced left ventricular function.

Design: A prospective, controlled, clinical study.

Setting: Medical intensive care unit in a university hospital.

Patients: A total of 18 sedated, mechanically ventilated, and moderately hypovolemic intensive care unit patients, eight with reduced left ventricular function (ejection fraction area, 24.9+/-8.0%, group A), ten with normal left ventricular function (ejection fraction area, 57.6+/-13.0%, group B).

Interventions: Continuous crystalloid infusion over 120 mins at a constant rate of 8 mL/kg/30 mins.

Measurements and main results: Stroke volume index, central venous pressure, pulmonary artery occlusion pressure (PAOP), TEDV, and ITBV were determined simultaneously at baseline and serially every 30 mins during continuous crystalloid infusion. A similar series of measurements was obtained during control conditions. Performance of various variables during fluid administration was assessed by time correlation analysis. Sensitivity for various variables defined as the ability to detect increasing amounts of administered fluid in individual patients was calculated. All examined variables increased during fluid administration and were unaffected during the control period. Mean time correlation (r2) was significantly higher for pressure monitoring (central venous pressure, r2 = 0.8281; PAOP, r2 = 0.5476) than for volume variables (TEDV, r2 = 0.0256; ITBV, r2 = 0.0729) in group A and was high for all variables in group B (central venous pressure, r2 = 0.7056; PAOP, r2 = 0.6241; TEDV, r2 = 0.49; ITBV, r2 = 0.4225). Sensitivities for central venous pressure, PAOP, TEDV, and ITBV after 120 min were 63%, 75%, 25%, and 25% in group A and 90%, 100%, 60%, and 60% in group B, respectively.

Conclusion: This study demonstrates limitations of the transpulmonary indicator dilution technique for monitoring of intravascular volume in patients with reduced left ventricular function.